1. FIELD OF THE INVENTION
The present invention relates to a casing for a magnetic tape cassette used for an audio system or a video system.
2. DESCRIPTION OF THE PRIOR ART
A casing for a magnetic tape cassette for an audio system or a video system has been prepared by molding to form a single or two-colored, single-layered structure.
FIG. 2 shows an audio magnetic tape cassette having a single colored, single-layered structure, in which FIG. 2A is a plan view of the outer surface side of an upper half casing; FIG. 2B is a plan view of the inner surface side of a lower half casing; and FIG. 2C is a cross-sectional view taken along a line X--X of the lower half casing. In FIG. 2, a reference numeral 10 designates an upper half casing consisting generally of a rectangular upper surface plate 12 around which vertical side walls having substantially uniform height (not shown) are formed. The upper surface plate 12 is provided with a rectangular tape-quantity observing window 14 at its central portion and a pair of reel driving shaft insertion holes 16a, 16b at a symmetrical position of right and left sides of the window 14. Generally, recesses 18, 20 for labelling areas to show A or B surface and other information in an elongated form extending in the right and left directions are provided in the upper and lower portions of the window 14. The upper surface plate 12 is further provided with a table-shaped projection 21 at the front side in the central portion to form a front opening part, a pair of cassette position determining holes 22a, 22b at right and left sides of the front opening part in a symmetrical manner, and a pair of capstan insertion holes 24a, 24b at a symmetrical position on either side of the cassette position determining holes 22a, 22b. Screw fastening holes 26a-26d are formed at four corners of the upper surface plate 12 and a screw fastening hole 26e is formed at the front side of the window 14 in the upper surface plate 12. Each of the screw fastening holes is provided with a countersink for receiving the head portion of a screw.
A lower half casing 28 comprises a rectangular bottom surface plate 32 having vertical side walls 30 of substantially uniform height. The bottom surface plate 32 is provided with a rectangular tape-quantity observing window 34 at the central portion and a pair of reel driving shaft insertion holes 36a, 36b at symmetrical positions at right and left sides of the window 34. There are respectively formed hub controlling ribs 37a, 37b around the reel driving shaft insertion holes 36a, 36b, lining sheet position determining pins 38a, 38b at symmetrical positions in the vertical direction of the window 34, and recesses 40, 42 for labelling areas to show A or B surface and other information of an elongated form extending in the right and left directions, the recesses being formed in the outer surface at upper and lower portions of the window 34. The lining sheet position determining pins 38a are in a cylindrical form so as to increase rigidity of the lower half casing whereby twisting or curving of the casing can be avoided. A central opening portion 44 is formed at the front side of the central portion of the bottom surface plate 32. A pad supporting means is provided near the central opening portion 44. At symmetrical positions of both sides of the central opening portion 44, there are formed a pair of cassette position determining holes 46a, 46b, a pair of capstan insertion holes 48a, 48b, and a pair of recesses for receiving tape guiding roller shafts 50a, 50b, respectively. Cylindrical projections for screw fastening 52a- 52e are formed at four corners and at the front side in the central portion of the bottom surface plate 32, numerals 54a,54b designate recesses for prevention of erroneous erasing which are provided at symmetrical positions of right and left sides of the inner portion of the bottom surface plate 32, and a numeral 56 designates a pawl formed in each of the recesses.
The upper and lower half casings 10, 28 are respectively formed by injection-molding of a material such as styrol resin. The upper and lower half casings 10, 28 are respectively opaque or transparent in a single color (generally in black) and have a single-layered structure. Each of the windows 14, 34 of the upper and lower half casings 10, 28 is attached with a transparent or semitransparent plastic plate 56 or 60 of polyethylene terephthalate (PET), polypropylene (PP), hard vinyl chloride (PVC) and so on after the injection-molding. The magnetic tape cassette is assembled by receiving a magnetic tape wound on hubs and other elements in a space formed by matching the upper and lower half casings 10, 28, and by fastening the half casings with tapping screws, the screw fastening portions being formed at four corners and at the front sides of the central portion of the upper and bottom surface plates 12, 34. Namely, the screw fastening holes 26 and the cylindrical projections for screw fastening 52 are fastened by screws.
FIG. 3 shows a two-colored, single-layered audio magnetic tape cassette casing, in which FIG. 3A is a plan view showing the outer surface of an upper half casing; FIG. 3B is a plan view showing the inner surface of a lower half casing; and FIG. 3C is a cross-sectional view taken along a line Y-Y in FIG. 3B. As apparent from FIGS. 2 and 3, the construction of the single colored, single-layered audio magnetic tape cassette casing is identical with that of the two-colored, single-layered one except for the construction of the window. In FIG. 3, a reference numeral 60 designates an upper half casing; a numeral 62 designates an upper surface plate; numerals 64a, 64b designate a pair of reel driving shaft insertion holes formed at a symmetrical position with respect to the vertical center line (not shown) of the upper surface plate 62 in FIG. 3A; a numeral 66 designates a tape-quantity observing window which includes the holes 64a, 64b and extends in the right and left directions in an elongated form.
A reference numeral 68 designates a lower half casing; a numeral 70 designates a bottom surface plate; numerals 72a, 72b designate a pair of reel driving shaft insertion holes formed at a symmetrical position with respect to the center line of the bottom surface plate 70 in FIG. 3B; and a numeral 74 designates a tape-quantity observing window which includes the reel driving shaft insertion holes 72a, 72b and extends in the right and left directions in an elongated form. The upper and lower half casings 60, 68 have respectively a two-colored, single-layered structure in which the windows 66, 74 are formed by injection-molding of transparent or semitransparent plastic resin and the other portion is formed by injection-molding of opaque plastic resin (generally in black) so that the transparent or semitransparent portion is integrally jointed to the opaque portion.
In the conventional magnetic tape cassette, the upper and lower casings must respectively be complicated in shape and construction to satisfactorily attain function of the magnetic tape cassette, and they are formed by molding a resinous material into a one-piece body. Accordingly, there are various projections, recesses and portions having different thickness in the upper and bottom surface plates of the both half casings. In a resinous product formed by injection-molding, the curing speed in a thin-walled portion is faster than that in a thick-walled portion. Therefore, a concave is produced in the vicinity of the thick-walled portion contiguous to the thin-walled portion due to shrinkage caused at the time of curing of the resin immediately after the injection-molding.
FIG. 4 is a cross-sectional view of the upper left portion of the lower half casing shown in FIG. 2B or FIG. 3B, in which a concave 76 is produced at the portion between the thick-walled portion where a cylindrical projection 52a for receiving a screw is formed and the recess for prevention of erroneous erasing 54a as a thin-walled portion contiguous to the thick-walled portion. When such concave is produced, flatness in a reference surface required for the half casings and other portions is impaired thereby causing irregular running of a magnetic tape. Further, there results a reduction in appearance of the casings due to poor glossiness.